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1.
A. Grimberg D. S. Burnett P. Bochsler H. Baur R. Wieler 《Space Science Reviews》2007,130(1-4):293-300
We discuss data of light noble gases from the solar wind implanted into a metallic glass target flown on the Genesis mission.
Helium and neon isotopic compositions of the bulk solar wind trapped in this target during 887 days of exposure to the solar
wind do not deviate significantly from the values in foils of the Apollo Solar Wind Composition experiments, which have been
exposed for hours to days. In general, the depth profile of the Ne isotopic composition is similar to those often found in
lunar soils, and essentially very well reproduced by ion-implantation modelling, adopting the measured velocity distribution
of solar particles during the Genesis exposure and assuming a uniform isotopic composition of solar wind neon. The results
confirm that contributions from high-energy particles to the solar wind fluence are negligible, which is consistent with in-situ
observations. This makes the enigmatic “SEP-Ne” component, apparently present in lunar grains at relatively large depth, obsolete.
20Ne/ 22Ne ratios in gas trapped very near the metallic glass surface are up to 10% higher than predicted by ion implantation simulations.
We attribute this superficially trapped gas to very low-speed, current-sheet-related solar wind, which has been fractionated
in the corona due to inefficient Coulomb drag. 相似文献
2.
R. C. Wiens D. S. Burnett C. M. Hohenberg A. Meshik V. Heber A. Grimberg R. Wieler D. B. Reisenfeld 《Space Science Reviews》2007,130(1-4):161-171
The Genesis mission returned samples of solar wind to Earth in September 2004 for ground-based analyses of solar-wind composition,
particularly for isotope ratios. Substrates, consisting mostly of high-purity semiconductor materials, were exposed to the
solar wind at L1 from December 2001 to April 2004. In addition to a bulk sample of the solar wind, separate samples of coronal
hole (CH), interstream (IS), and coronal mass ejection material were obtained. Although many substrates were broken upon landing
due to the failure to deploy the parachute, a number of results have been obtained, and most of the primary science objectives
will likely be met. These objectives include He, Ne, Ar, Kr, and Xe isotope ratios in the bulk solar wind and in different
solar-wind regimes, and 15N/14N and 18O/17O/16O to high precision. The greatest successes to date have been with the noble gases. Light noble gases from bulk solar wind
and separate solar-wind regime samples have now been analyzed. Helium results show clear evidence of isotopic fractionation
between CH and IS samples, consistent with simplistic Coulomb drag theory predictions of fractionation between the photosphere
and different solar-wind regimes, though fractionation by wave heating is also a possible explanation. Neon results from closed
system stepped etching of bulk metallic glass have revealed the nature of isotopic fractionation as a function of depth, which
in lunar samples have for years deceptively suggested the presence of an additional, energetic component in solar wind trapped
in lunar grains and meteorites. Isotope ratios of the heavy noble gases, nitrogen, and oxygen are in the process of being
measured. 相似文献
3.
Wiens Roger C. Neugebauer Marcia Reisenfeld Daniel B. Moses Ronald W. Nordholt Jane E. Burnett Donald S. 《Space Science Reviews》2003,105(3-4):601-626
The design and operation of the Genesis Solar-Wind Concentrator relies heavily on computer simulations. The computer model
is described here, as well as the solar wind conditions used as simulation inputs, including oxygen charge state, velocity,
thermal, and angular distributions. The simulation included effects such as ion backscattering losses, which also affect the
mass fractionation of the instrument. Calculations were performed for oxygen, the principal element of interest, as well as
for H and He. Ion fluences and oxygen mass fractionation are determined as a function of radius on the target. The results
were used to verify that the instrument was indeed meeting its requirements, and will help prepare for distribution of the
target samples upon return of the instrument to earth. The actual instrumental fractionation will be determined at that time
by comparing solar-wind neon isotope ratios measured in passive collectors with neon in the Concentrator target, and by using
a model similar to the one described here to extrapolate the instrumental fractionation to oxygen isotopes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
The Sun is the largest reservoir of matter in the solar system, which formed 4.6 Gyr ago from the protosolar nebula. Data
from space missions and theoretical models indicate that the solar wind carries a nearly unfractionated sample of heavy isotopes
at energies of about 1 keV/amu from the Sun into interplanetary space. In anticipation of results from the Genesis mission’s
solar-wind implanted samples, we revisit solar wind isotopic abundance data from the high-resolution CELIAS/MTOF spectrometer
on board SOHO. In particular, we evaluate the isotopic abundance ratios 15N/14N, 17O/16O, and 18O/16O in the solar wind, which are reference values for isotopic fractionation processes during the formation of terrestrial planets
as well as for the Galactic chemical evolution. We also give isotopic abundance ratios for He, Ne, Ar, Mg, Si, Ca, and Fe
measured in situ in the solar wind. 相似文献
5.
J. C. Raymond 《Space Science Reviews》1999,87(1-2):55-66
Order of magnitude variations in relative elemental abundances are observed in the solar corona and solar wind. The instruments
aboard SOHO make it possible to explore these variations in detail to determine whether they arise near the solar surface
or higher in the corona. A substantial enhancement of low First Ionization Potential (FIP) elements relative to high FIP elements
is often seen in both the corona and the solar wind, and that must arise in the chromosphere. Several theoretical models have
been put forward to account for the FIP effect, but as yet even the basic physical mechanism responsible remains an open question.
Evidence for gravitational settling is also found at larger heights in quiescent streamers. The question is why the heavier
elements don't settle out completely.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
Roger C. Wiens Daniel B. Reisenfeld Chad Olinger Peter Wurz Veronika S. Heber Donald S. Burnett 《Space Science Reviews》2013,175(1-4):93-124
The Genesis mission Solar Wind Concentrator was built to enhance fluences of solar wind by an average of 20x over the 2.3 years that the mission exposed substrates to the solar wind. The Concentrator targets survived the hard landing upon return to Earth and were used to determine the isotopic composition of solar-wind—and hence solar—oxygen and nitrogen. Here we report on the flight operation of the instrument and on simulations of its performance. Concentration and fractionation patterns obtained from simulations are given for He, Li, N, O, Ne, Mg, Si, S, and Ar in SiC targets, and are compared with measured concentrations and isotope ratios for the noble gases. Carbon is also modeled for a Si target. Predicted differences in instrumental fractionation between elements are discussed. Additionally, as the Concentrator was designed only for ions ≤22 AMU, implications of analyzing elements as heavy as argon are discussed. Post-flight simulations of instrumental fractionation as a function of radial position on the targets incorporate solar-wind velocity and angular distributions measured in flight, and predict fractionation patterns for various elements and isotopes of interest. A tighter angular distribution, mostly due to better spacecraft spin stability than assumed in pre-flight modeling, results in a steeper isotopic fractionation gradient between the center and the perimeter of the targets. Using the distribution of solar-wind velocities encountered during flight, which are higher than those used in pre-flight modeling, results in elemental abundance patterns slightly less peaked at the center. Mean fractionations trend with atomic mass, with differences relative to the measured isotopes of neon of +4.1±0.9 ‰/amu for Li, between ?0.4 and +2.8 ‰/amu for C, +1.9±0.7‰/amu for N, +1.3±0.4 ‰/amu for O, ?7.5±0.4 ‰/amu for Mg, ?8.9±0.6 ‰/amu for Si, and ?22.0±0.7 ‰/amu for S (uncertainties reflect Monte Carlo statistics). The slopes of the fractionation trends depend to first order only on the relative differential mass ratio, Δm/m. This article and a companion paper (Reisenfeld et al. 2012, this issue) provide post-flight information necessary for the analysis of the Genesis solar wind samples, and thus serve to complement the Space Science Review volume, The Genesis Mission (v. 105, 2003). 相似文献
7.
Ester Antonucci 《Space Science Reviews》2006,124(1-4):35-50
The dynamics of the solar corona as observed during solar minimum with the Ultraviolet Coronagraph Spectrometer, UVCS, on
SOHO is discussed. The large quiescent coronal streamers existing during this phase of the solar cycle are very likely composed
by sub-streamers, formed by closed loops and separated by open field lines that are channelling a slow plasma that flows close
to the heliospheric current sheet. The polar coronal holes, with magnetic topology significantly varying from their core to
their edges, emit fast wind in their central region and slow wind close to the streamer boundary. The transition from fast
to slow wind then appears to be gradual in the corona, in contrast with the sharp transition between the two wind regimes
observed in the heliosphere. It is suggested that speed, abundance and kinetic energy of the wind are modulated by the topology
of the coronal magnetic field. Energy deposition occurs both in the slow and fast wind but its effect on the kinetic temperature
and expansion rate is different for the slow and fast wind. 相似文献
8.
R. A. Mewaldt C. M. S. Cohen G. M. Mason A. C. Cummings M. I. Desai R. A. Leske J. Raines E. C. Stone M. E. Wiedenbeck T. T. von Rosenvinge T. H. Zurbuchen 《Space Science Reviews》2007,130(1-4):207-219
Although the average composition of solar energetic particles (SEPs) and the bulk solar wind are similar in a number of ways,
there are key differences which imply that solar wind is not the principal seed population for SEPs accelerated by coronal
mass ejection (CME) driven shocks. This paper reviews these composition differences and considers the composition of other
possible seed populations, including coronal material, impulsive flare material, and interplanetary CME material. 相似文献
9.
Radio occultation, ultraviolet, and white-light measurements have expanded our knowledge of the morphology of density and
velocity in polar coronal holes, and made it possible to carry out the first systematic comparisons between the Ulysses solar wind measurements and quantitative white-light observations of the solar corona. This paper summarizes the rationale
and salient features of this new approach which has been used to relate the solar wind observed by Ulysses in 1993–1995 to the inner corona. The statistical characteristics (average, standard deviation, and autocorrelation function)
of the Ulysses density measurements of the fast wind are found to be mirrored in those of polarized brightness measurements of path-integrated
density made by the High Altitude Observatory (HAO) Mauna Loa K-coronagraph at 1.15 R
⊙. These results reinforce the conclusions from comparisons between measurements of the outer and inner corona. They show that
the polar coronal hole extends radially into the solar wind, and that sources of the fast wind are not limited to coronal
holes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
R. Kallenbach F.M. Ipavich H. Kucharek P. Bochsler A.B. Galvin J. Geiss F. Gliem G. Gloeckler H. Grünwaldt S. Hefti M. Hilchenbach D. Hovestadt 《Space Science Reviews》1998,85(1-2):357-370
Using the high-resolution mass spectrometer CELIAS/MTOF on board SOHO we have measured the solar wind isotope abundance ratios
of Si, Ne, and Mg and their variations in different solar wind regimes with bulk velocities ranging from 330 km/s to 650 km/s.
Data indicate a small systematic depletion of the heavier isotopes in the slow solar wind on the order of (1.4±1.3)% per amu
(2σ-error) compared to their abundances in the fast solar wind from coronal holes. These variations in the solar wind isotopic
composition represent a pure mass-dependent effect because the different isotopes of an element pass the inner corona with
the same charge state distribution. The influence of particle mass on the acceleration of minor solar wind ions is discussed
in the context of theoretical models and recent optical observations with other SOHO instruments.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
11.
Observations in the solar wind have revealed important insights into how energetic particles are accelerated in astrophysical
plasmas. In circumstances where stochastic acceleration is expected, a suprathermal tail on the distribution function is formed
with a common spectral shape: the spectrum is a power law in particle speed with a spectral index of −5. Recent theories for
this phenomenon, in which thermodynamic constraints are applied to explain the common spectral shape, are reviewed. As an
example of potential extensions of this theoretical work, consideration is given to the acceleration of Anomalous Cosmic Rays
in the heliosheath. 相似文献
12.
The solar wind charge state and elemental compositions have been measured with the Solar Wind Ion Composition Spectrometers
(SWICS) on Ulysses and ACE for a combined period of about 25 years. This most extensive data set includes all varieties of
solar wind flows and extends over more than one solar cycle. With SWICS the abundances of all charge states of He, C, N, O,
Ne, Mg, Si, S, Ar and Fe can be reliably determined (when averaged over sufficiently long time periods) under any solar wind
flow conditions. Here we report on results of our detailed analysis of the elemental composition and ionization states of
the most unbiased solar wind from the polar coronal holes during solar minimum in 1994–1996, which includes new values for
the abundance S, Ca and Ar and a more accurate determination of the 20Ne abundance. We find that in the solar minimum polar coronal hole solar wind the average freezing-in temperature is ∼1.1×106 K, increasing slightly with the mass of the ion. Using an extrapolation method we derive photospheric abundances from solar
wind composition measurements. We suggest that our solar-wind-derived values should be used for the photospheric ratios of
Ne/Fe=1.26±0.28 and Ar/Fe=0.030±0.007. 相似文献
13.
V. S. Heber R. C. Wiens D. B. Reisenfeld J. H. Allton H. Baur D. S. Burnett C. T. Olinger U. Wiechert R. Wieler 《Space Science Reviews》2007,130(1-4):309-316
The concentrator on Genesis provided samples of increased fluences of solar wind ions for precise determination of the oxygen
isotopic composition. The concentration process caused mass fractionation as a function of the radial target position. This
fractionation was measured using Ne released by UV laser ablation and compared with modelled Ne data, obtained from ion-trajectory
simulations. Measured data show that the concentrator performed as expected and indicate a radially symmetric concentration
process. Measured concentration factors are up to ∼30 at the target centre. The total range of isotopic fractionation along
the target radius is 3.8%/amu, with monotonically decreasing 20Ne/22Ne towards the centre, which differs from model predictions. We discuss potential reasons and propose future attempts to overcome
these disagreements. 相似文献
14.
D. B. Reisenfeld D. S. Burnett R. H. Becker A. G. Grimberg V. S. Heber C. M. Hohenberg A. J. G. Jurewicz A. Meshik R. O. Pepin J. M. Raines D. J. Schlutter R. Wieler R. C. Wiens T. H. Zurbuchen 《Space Science Reviews》2007,130(1-4):79-86
Analysis of the Genesis samples is underway. Preliminary elemental abundances based on Genesis sample analyses are in good
agreement with in situ-measured elemental abundances made by ACE/SWICS during the Genesis collection period. Comparison of
these abundances with those of earlier solar cycles indicates that the solar wind composition is relatively stable between
cycles for a given type of flow. ACE/SWICS measurements for the Genesis collection period also show a continuum in compositional
variation as a function of velocity for the quasi-stationary flow that defies the simple binning of samples into their sources
of coronal hole (CH) and interstream (IS). 相似文献
15.
This paper contains a summary of the topics treated in the working group on abundance variations in the solar atmosphere and in the solar wind. The FIP bias (overabundance of particles with low First Ionization Potentials over photospheric abundances) in coronal holes and coronal hole associated solar wind amounts to values between 1 and 2. The FIP bias in the slow solar wind is typically a factor 4, consistent with optical observations in streamers. In order to distinguish between different theoretical models which make an attempt to explain the FIP bias, some observable parameters must be provided. Unfortunately, many models are deficient in this respect. In addition to FIP fractionation, gravitational settling of heavy elements has been found in the core of long lived streamers. The so-called electron 'freeze in' temperatures derived from in situ observed ionization states of minor ions in the fast wind are significantly higher than the electron temperatures derived from diagnostic line ratios observed in polar coronal holes. The distinction between conditions in plumes and interplume lanes needs to be further investigated. The 'freeze in' temperatures for the slow solar wind are consistent with the electron temperatures derived for streamers. This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
16.
Wohlmuth R. Plettemeier D. Edenhofer P. Bird M.K. Efimov A.I. Andreev V.E. Samoznaev L.N. Chashei I.V. 《Space Science Reviews》2001,97(1-4):9-12
Temporal power spectra have been computed from recordings of the downlink frequency fluctuations of the Galileo and Ulysses radio signals during their solar conjunctions. Both the equatorial streamer belt and the polar coronal holes were investigated
over a range of ray path solar offset distances from 4 to 80 R⊙. By combining gapless data from successive tracking passes, Doppler scintillation power spectra could be computed down to
extremely low frequencies. Some spectra feature a low-frequency turnover at frequencies around 0.1 mHz that could be interpreted
as an outer scale of density turbulence in the coronal plasma.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
A. Sprague J. Warell G. Cremonese Y. Langevin J. Helbert P. Wurz I. Veselovsky S. Orsini A. Milillo 《Space Science Reviews》2007,132(2-4):399-431
Mercury’s surface is thought to be covered with highly space-weathered silicate material. The regolith is composed of material
accumulated during the time of planetary formation, and subsequently from comets, meteorites, and the Sun. Ground-based observations
indicate a heterogeneous surface composition with SiO2 content ranging from 39 to 57 wt%. Visible and near-infrared spectra, multi-spectral imaging, and modeling indicate expanses
of feldspathic, well-comminuted surface with some smooth regions that are likely to be magmatic in origin with many widely
distributed crystalline impact ejecta rays and blocky deposits. Pyroxene spectral signatures have been recorded at four locations.
Although highly space weathered, there is little evidence for the conversion of FeO to nanophase metallic iron particles (npFe0), or “iron blebs,” as at the Moon. Near- and mid-infrared spectroscopy indicate clino- and ortho-pyroxene are present at
different locations. There is some evidence for no- or low-iron alkali basalts and feldspathoids. All evidence, including
microwave studies, point to a low iron and low titanium surface. There may be a link between the surface and the exosphere
that may be diagnostic of the true crustal composition of Mercury. A structural global dichotomy exists with a huge basin
on the side not imaged by Mariner 10. This paper briefly describes the implications for this dichotomy on the magnetic field
and the 3 : 2 spin : orbit coupling. All other points made above are detailed here with an account of the observations, the
analysis of the observations, and theoretical modeling, where appropriate, that supports the stated conclusions. 相似文献
18.
T. H. Zurbuchen S. Hefti L. A. Fisk G. Gloeckler R. Von Steiger 《Space Science Reviews》1999,87(1-2):353-356
The transition between coronal hole associated fast solar wind and slow solar wind is studied using data from the high resolution
mass spectrometer SWICS on ACE. We discuss the data in the framework of a recent theory about the global heliospheric magnetic
field and conclude that the data are consistent with magnetic connections between field-lines in the fast and in the slow
wind.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
19.
von Steiger R. Zurbuchen T.H. Geiss J. Gloeckler G. Fisk L.A. Schwadron N.A. 《Space Science Reviews》2001,97(1-4):123-127
The source region of solar wind plasma is observed to be directly reflected in the compositional pattern of both elemental
and charge state compositions. Slow solar wind associated with streamers shows higher freeze-in temperatures and larger FIP
enhancements than coronal hole associated wind. Also, the variability of virtually all compositional parameters is much higher
for slow solar wind compared to coronal hole associated wind. We show that these compositional patterns persist even though
stream-stream interactions complicate the identification based on in situ plasma parameters.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
Barraclough B.L. Dors E.E. Abeyta R.A. Alexander J.F. Ameduri F.P. Baldonado J.R. Bame S.J. Casey P.J. Dirks G. Everett D.T. Gosling J.T. Grace K.M. Guerrero D.R. Kolar J.D. Kroesche J.L. Lockhart W.L. McComas D.J. Mietz D.E. Roese J. Sanders J. Steinberg J.T. Tokar R.L. Urdiales C. Wiens R.C. 《Space Science Reviews》2003,105(3-4):627-660
The Genesis Ion Monitor (GIM) and the Genesis Electron Monitor (GEM) provide 3-dimensional plasma measurements of the solar
wind for the Genesis mission. These measurements are used onboard to determine the type of plasma that is flowing past the
spacecraft and to configure the solar wind sample collection subsystems in real-time. Both GIM and GEM employ spherical-section
electrostatic analyzers followed by channel electron multiplier (CEM) arrays for detection and angle and energy/charge analysis
of incident ions and electrons. GIM is of a new design specific to Genesis mission requirements whereas the GEM sensor is
an almost exact copy of the plasma electron sensors currently flying on the ACE and Ulysses spacecraft, albeit with new electronics
and programming. Ions are detected at forty log-spaced energy levels between ∼ 1 eV and 14 keV by eight CEM detectors, while
electrons with energies between ∼ 1 eV and 1.4 keV are measured at twenty log-spaced energy levels using seven CEMs. The spin
of the spacecraft is used to sweep the fan-shaped fields-of-view of both instruments across all areas of the sky of interest,
with ion measurements being taken forty times per spin and samples of the electron population being taken twenty four times
per spin. Complete ion and electron energy spectra are measured every ∼ 2.5 min (four spins of the spacecraft) with adequate
energy and angular resolution to determine fully 3-dimensional ion and electron distribution functions. The GIM and GEM plasma
measurements are principally used to enable the operational solar wind sample collection goals of the Genesis mission but
they also provide a potentially very useful data set for studies of solar wind phenomena, especially if combined with other
solar wind data sets from ACE, WIND, SOHO and Ulysses for multi-spacecraft investigations.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献